The invention relates to printing with custom colors in an inkjet printing system. It finds particular application in conjunction with incorporating machine-readable color ink supply tanks, mixing inks from multiple ink supply tanks to create custom colors, and printing with custom colors in an inkjet printing system and will be described with particular reference thereto. However, it is to be appreciated that the invention is also amenable to other applications.
Known methods and apparatus for mixing colorants to achieve a desired target color in pigment-based and dye-based applications involve human interaction, namely determining if the mixed colorants match the target color by visual inspection. For example, an experienced attendant of a paint mixing machine in a home improvement store will begin with a base color and add one or more other colors to achieve a customer's desired color. The attendant may refer to a predetermined paint mixing guide to determine which colors and how much of each color to add to the base color before beginning the mixing process. Alternatively, the attendant may access color formulations stored in a memory of a computer or similar device. After the paint is thoroughly mixed, the attendant will visually inspect the resulting color and confirm it matches the desired color. Alternatively reflectance spectra can be obtained using a free standing spectrophotometer and a “recipe” for mixing the desired color. Again the attendant will mix the color and confirm the match.
More human interaction is required in the case of colors that have faded or otherwise been transformed, e.g., due to environmental exposure such as solar radiation or a saltwater environment. In these cases, although the identity and proportions of colorants comprising the original color designation may be known, the target color that must be matched is actually a variation (usually a lighter shade) of the original color. In general, achieving the target color in these cases requires repeated mixing and visual inspection steps, because there is no guide that can be consulted. Here the spectrophotometric approach is the only tenable guide except for visual matching by the attendant.
Other areas in which color mixing is carried out on a trial and error basis with visual inspection include offset printing, wallpapers, fabric coloring and automobile painting, among others. In offset printing, a printer seeking to match a special color relies on industry standard color matching systems to match the special color. Common systems include those published by Pantone and Sun Printing Inks.
It is well known that conventional inkjet printing processes can be adapted to produce multicolor images. For example, an input image may be divided into a series of color separated images corresponding to the primary colors in the input image. Each color separated image is printed with a complimentary ink marking material in a primary color or a colorant which is the subtractive compliment of the color separated image, with each printed color separated image subsequently superimposed, in registration, on one another to produce a multicolor image output. Thus, a multicolor image is generated from patterns of different primary colors or their subtractive compliments that are blended by the eye to create a visual perception of a color image.
This procedure of separating and superimposing color images produces so-called “process color” images, wherein each color separated image comprises an arrangement of picture elements, or pixels, corresponding to a spot to be developed with ink marking material of a particular color. The multicolor image is a mosaic of different color pixels, wherein the color separations are laid down in the form of halftone dots. In halftone image processing, the dot sizes and/or spatial densities of each of the color components making up the multicolor image can be altered to produce a large variation of color hues and shades. For example, lighter tints can be produced by reducing the dot size or spatial densities such that a greater amount of white from the page surface remains uncovered to reflect light to the eye. Likewise, darker shades can be produced by increasing the dot size or spatial densities. This method of generating process color images by overlapping halftones of different colors corresponding to the primary colors or their subtractive equivalents is well known in the art and will not be further described herein. The range of colors that can be produced by this process is determined by the number of primary colors that are used and the colors of those primaries. Generally a four-color process is employed using cyan, magenta, yellow and black primaries. Other systems using more primary inks are also known and are referred to by names such as “hyper color”, “HiFi Color,” IndiColor™ and the like. These systems allow a wider range or gamut of colors to be produced.
With the capabilities of digital printing moving into multicolor imaging, advances have also been directed to the creation of so-called “highlight color” images, wherein independent, differently colored, monochrome images are created on a single output copy sheet, preferably in a single processing cycle. Likewise, “spot color” and/or “high-fidelity” color printing has been developed, wherein a printing system capable of producing process color output images is augmented with additional inkjet cartridges containing additional primary colors beyond the usual four primaries colors used to produce the process color output. These additional inkjet cartridges are used for extending the color gamut of the process color output (high fidelity color), and thereby more closely emulate standardized spot colors, such as those defined by Pantone. As such, several concepts derived from conventional inkjet imaging techniques which were previously directed to monochrome and/or process color image formation have been modified to generate output images having selected areas that are different in color than the rest of the document. Applications of highlight color include, for example, emphasis on important information, accentuation of titles, and more generally, differentiation of specific areas of text or other image information.
One specific application of highlight color processing is customer selectable color printing, wherein a very specific highlight color is required. Customer selectable colors are typically utilized to provide instant identification and authenticity to a document. As such, the customer is usually highly concerned that the color meets particular color specifications. For example, the red color associated with Xerox' digital stylized “X” is a customer selectable color having a particular shade, hue and color value. Likewise, the particular shade of orange associated with Syracuse University is a good example of a customer selectable color. A more specialized example of a customer selectable color output can be found in the field of “custom color,” which specifically refers to registered proprietary colors, as used, for example, in corporate logos, authorized letterhead and official seals. The yellow associated with Kodak brand products, and the brown associated with Hershey brand products are good examples of custom colors which are required to meet exacting color standards in a highlight color or spot color printing application.
A significant number of customer selectable colors cannot be accurately generated via halftone process color based on the standard four-color methods because the production of solid image areas of a particular color using halftone image processing techniques. Additionally the half tone process yields nonuniformity of the color in the image area which can be objectionable in some applications. Further, lines and text produced by halftone process color are very sensitive to misregistration of the multiple color images such that blurring, color variances, and other image quality defects may result.
As a result of the deficiencies noted above, it would be desirable for customer selectable color production in inkjet printing systems to be carried out by providing a singular premixed developing material composition made up of a mixture of multiple color inks blended in preselected concentrations for producing the desired customer selectable color output. Methods for mixing multiple color inks to produce a particular color printing material would be analogous to processes used to produce customer selectable color paints and inks for offset printing. In offset printing, for example, a customer selectable color output image can be produced by printing a solid image pattern with a premixed customer selectable color printing ink as opposed to printing a plurality of halftone image patterns with various primary colors or compliments thereof.
Customer selectable color printing materials including paints, printing inks and developing materials can be manufactured by determining precise amounts of constituent basic color components making up a given customer selectable color material, providing precisely measured amounts of each constituent basic color component, and thoroughly mixing these color components. This process is commonly facilitated by reference to a color guide or swatch book containing hundreds or even thousands of swatches illustrating different colors, wherein each color swatch is associated with a specific formulation of colorants. Probably the most popular of these color guides is published by Pantone®, Inc. of Moonachie, N.J. The Pantone® Color Formula Guide expresses colors using a certified matching system and provides the precise formulation necessary to produce a specific customer selectable color by physically intermixing predetermined concentrations of up to four colors from a set of up to 18 principal or basic colors. There are many colors available using the Pantone® system or other color formula guides of this nature that cannot be produced via typical halftone process color methods or even by mixing selected amounts of cyan, magenta, yellow and/or black inks or developing materials.
The following disclosures may be relevant to some aspects of the invention:                U.S. Pat. No. 5,781,828 to Caruthers, Jr. et al., Liquid Color Mixing And Replenishment System For An Electrostatographic Printing Machine;        U.S. Pat. No. 5,892,891 to Dalal et al., System For Printing Color Images With Extra Colorants In Addition To Primary Colorants;        U.S. Pat. No. 5,897,239 to Caruthers, Jr. et al., Photometric Color Correction And Control System For Custom Colors;        U.S. Pat. No. 5,899,605 to Caruthers, Jr. et al., Color Mixing And Color System For Use In A Printing Machine;        U.S. Pat. No. 6,002,893 to Caruthers, Jr. et al., High And Low Pigment Loadings For Custom Colors;        U.S. Pat. No. 6,052,195 to Mestha et al., Automatic Colorant Mixing Method And Apparatus; and        U.S. Pat. No. 6,307,645 B1 to Mantell et al., Halftoning For Hi-Fi Color Inks.        
U.S. Pat. No. 5,781,828 discloses a system and method for color mixing management in an electrostatographic printing system, wherein a developing material reservoir containing an operative solution of colored developing material including a mixture of selected color components is continuously replenished with selected differently colored developing material concentrates in a predetermined ratio so as to be capable of producing a customer selectable color image area on an output substrate. The '828 patent also discloses the mixing of a customer selectable color in situ, either from stored proportions known to compensate for developability differences or from approximate amounts of primary color components initially deposited and mixed in the developing material reservoir with the resultant operative developing material mixture continually developed and replenished with a predetermined ratio of color components until the developing material mixture reaches a steady state color.
U.S. Pat. No. 5,892, 891 discloses a “hi-fi” color printing system, wherein colorants beyond the regular CMYK primary colorants are available, a main gamut obtainable with the CMYK colorants only is mutually exclusive with at least one extended gamut in which a hi-fi colorant is used and a complementary one of the CMY colorants is excluded. Because the main and extended gamuts are mutually exclusive, no more than four colorants are used in any part of the image, and no more than four halftone screens need be used to obtain any desired color.
U.S. Pat. No. 5,897,239 discloses a system and method for color mixing control in a developing material-based electrostatographic printing system. A developing reservoir containing an operative solution of customer selectable colored developing material is continuously replenished with selectively variable amounts of basic color components making up the operative solution by controlling the rate of replenishment of various color components added to the supply reservoir. An optical sensor is used to measure the optical spectrum of the developed image so that the actual optical spectrum thereof can be brought into agreement with a target optical spectrum associated with a customer selectable color. The '239 system may be used to mix a customer selectable color in situ, whereby approximate amounts of primary color components are initially deposited and mixed in the developing material reservoir and the resultant developed image is monitored and adjusted until the mixture reaches a target optical spectrum. An additional optical sensor may be used to control and maintain the color of the developing material in the reservoir through continuous monitoring and correction in order to maintain a particular ratio of color components in the reservoir over extended periods associated with very long print runs.
U.S. Pat. No. 5,899,605 discloses a system for determining, in real time, the precise color measurements of a colorant being applied in a printing apparatus, the colorant being a combination of two or more primary colorants. Light from a light source is transmitted through or reflected from the colorant mixture, and received by a sensor having a relatively small number of photo detectors, each photo detector having a different translucent primary-color filter thereon. Various special algorithms can be used to approach the accuracy of a spectrophotometer using a relatively simple light sensor.
U.S. Pat. No. 6,002,893 discloses custom color control techniques that are extended by using a high and a low pigment loaded toner for each color of the primary colors in the printing system. In one application, a large gamut of colors and fine control of color is accomplished by using a minimum number of colored pigments with each color incorporated into both high and low pigment loaded toners. Another application of the high/low pigment loaded toners is the ability to increase the developed mass per unit area (DMA) for rough papers without increasing pigment mass per unit area (PMA) by either mixing high and low pigment-loaded toners or by mixing a high pigment-loaded toner with an unpigmented toner to obtain the desired custom color. A novel sensor which senses fluorescent molecules in toner particles provides a color independent measure of total toner solids.
U.S. Pat. No. 6,052,195 discloses a method of mixing colorants to achieve a target color includes combining individual colorants, detecting an output color of the combined colorants with a color sensing device and automatically adjusting the output color based on comparison between the detected output color and the target color. An apparatus for mixing colorants according to this method is also disclosed.
U.S. Pat. No. 6,307,645 B1 discloses a hi-fi color printing system wherein an inverted halftone screen is provided having the same angle and frequency as a half-tone screen for an opposing color. The dots of the inverse halftone screen are configured to be located midway between the centers of the dots of the half-tone screen. The halftone screen and inverted halftone screen are used in the printing process to extend the gamut of colors within a printing system, render improved neutral colors, and provide an improved transition through neutral regions of color space. The '645 system allows for additional printing of multiple colors without the need for increasing the number of screens used in the image processing system.